You know the monster in Hyperion (D.Simmons' book) who can control time to suddenly appear here and there and nail poor mortal sinners like us?

I met something similar yesterday in a crowded Sedina B8: a ship appearing here and there on my screen, unhittable but able to hit me as if I was a sitting duck whereas I was dodging.

I would like to know if this is due only to (probably mutual?) lag or if something useful can be done with the program settings to alleviate those issues.

Its them lagging. It has a lovely side effect of making them invincible and you easy to hit (Since you arnt moving at all on thier screen) Theres a few players who use that to thier advantage. If you would like to try it yourself, get near your switch/modem/router, and pull your cable out then put it back in, out in, etc... while fighting. Youll have newfound invincibility.

True but ... I thought shots while lagged out no longer count as hits. Is that not true?

Actually, when lagged out, both people appear to "jump" on each others screens. Contrary to popular opinion, high ping does not give either party an advantage unless the target's movements are small and linear- IE: moving in a straight line like the frigate.

If they stutter thier connectivity it does give you an advantage. You update just enough to still score hits, and not enough to actually be where you are at any given point to your enemy. Try it sometime. They will only be able to hit in that split second after you teleport, and you will be able to hit them rather easily. Its due to the fact that yeah, vendetta doesnt score hits when you are lagging usually, but it doesnt realize you are lagging immediatly, so when you stutter it, you get the lag effect, without the cant hurt, cant get hit, lag-clause.